This invention relates to a core for a magnetic device such as an electromechanical switch. More particularly, a core is a plurality of strips of a magnetic material separated by a diamond-like, polycrystalline carbon coating.
High average power electronic devices requiring frequent pulsing such as linear induction accelerators for power station applications as well as high power microwave units utilize magnetic switches. The core of the magnetic switch is usually formed from a plurality of layers of a magnetic material separated by an electrically insulating inter-laminar material.
U.S. Pat. No. 4,368,447 to Inomata et al discloses forming a core by rolling a thin strip of an amorphous magnetic alloy into a coil. U.S. Pat. No. 4,447,795 to Sefko et al discloses a laminated magnetic core having a plurality of thin metallic strips bonded together and electrically insulated by a thin epoxy resin.
U.S. Pat. No. 4,983,859 to Nakajima et al, which is incorporated by reference in its entirety herein, discloses forming the core of a high power magnetic switch from a coil of an amorphous magnetic tape. A polyethylene terephthalate (MYLAR) film is disposed between the amorphous layers to provide electrical insulation. Rapid pulsing of the switch generates a substantial quantity of heat. To remove the heat, the core is divided into four separate spaced apart coils. A coolant flows around the outside of each coil and in the spaces separating the coils.
Even with cooling channels, the temperature at the center of the cores can reach 100.degree. C. Elevated temperature operation reduces the operating efficiency and effective lifetime of the switch. Further, the size of the core must be increased to provide space for the cooling channels. The packing fraction, that volume percent of the core occupied by the magnetic material and contributing to the effectiveness of the switch, is only about 70% in this type of switch.
Two requirements of the interlaminar material are high electrical resistivity and a high breakdown voltage. One material meeting these requirements is polycrystalline carbon, also known as diamond-like carbon. As disclosed in U.S. Pat. No. 5,126,206 to Garg et al, which is incorporated by reference in its entirety herein, a polycrystalline diamond layer can be deposited on a substrate by streaming a gaseous mixture containing a hydrocarbon past a heated filament under a vacuum, typically less than 100 torr. The resultant hydrocarbon radicals are deposited as a carbon film on a cooled substrate. Under proper conditions, a polycrystalline carbon, diamond-like coating, is deposited on the substrate. The polycrystalline carbon has high electrical resistivity, typically greater than 10.sup.6 ohm-cm and a high breakdown voltage, typically greater than 100 volts.
Polycrystalline diamond layers have been used to provide electrical isolation between electronic devices and U.S. Pat. No. 5,135,808 to Kimock et al discloses the use of a polycrystalline diamond layer to provide abrasion resistance to an optically transparent substrate. To date, the unique properties of polycrystalline carbon have not been applied to magnetic cores.